perf: open the masternode connection thread on demand

Masternodes, quorum watchers and wallet mixing with CoinJoin creates masternode connections.

Every node started the "mncon" thread though it should be spawn only when needed.
Plain nodes with wallets disabled no longer carry the thread and its 0.9 MB of thread-local storage.

Author: knst

src/init.cpp

@@ -2562,6 +2562,9 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
     connOptions.m_peer_connect_timeout = peer_connect_timeout;
     connOptions.socketEventsMode = ::g_socket_events_mode;
     connOptions.m_active_masternode = node.active_ctx != nullptr;
+    // wallets may mix with CoinJoin, which connects to the mixing masternode
+    connOptions.m_masternode_connections = node.active_ctx != nullptr || quorums_watch ||
+                                           node.wallet_loader != nullptr;
 
     // Port to bind to if `-bind=addr` is provided without a `:port` suffix.
     const uint16_t default_bind_port =

src/net.cpp

@@ -4093,10 +4093,11 @@ bool CConnman::Start(CDeterministicMNManager& dmnman, CMasternodeMetaMan& mn_met
             [this, connect = connOptions.m_specified_outgoing, &dmnman] { ThreadOpenConnections(connect, dmnman); });
     }
 
-    // Initiate masternode connections
-    threadOpenMasternodeConnections = std::thread(&util::TraceThread, "mncon", [this, &dmnman, &mn_metaman, &mn_sync] {
-        ThreadOpenMasternodeConnections(dmnman, mn_metaman, mn_sync);
-    });
+    if (m_masternode_connections) {
+        threadOpenMasternodeConnections = std::thread(&util::TraceThread, "mncon", [this, &dmnman, &mn_metaman, &mn_sync] {
+            ThreadOpenMasternodeConnections(dmnman, mn_metaman, mn_sync);
+        });
+    }
 
     // Process messages
     threadMessageHandler = std::thread(&util::TraceThread, "msghand", [this] { ThreadMessageHandler(); });

src/net.h

@@ -1245,6 +1245,9 @@ friend class CNode;
         SocketEventsMode socketEventsMode = SocketEventsMode::Select;
         bool m_i2p_accept_incoming;
         bool m_active_masternode = false;
+        //! Run the thread that opens connections to masternodes; only masternodes, quorum watchers and
+        //! CoinJoin mixing ever request them.
+        bool m_masternode_connections = true;
     };
 
     void Init(const Options& connOptions) EXCLUSIVE_LOCKS_REQUIRED(!m_added_nodes_mutex, !m_total_bytes_sent_mutex)
@@ -1283,6 +1286,7 @@ friend class CNode;
         socketEventsMode = connOptions.socketEventsMode;
         m_onion_binds = connOptions.onion_binds;
         m_active_masternode = connOptions.m_active_masternode;
+        m_masternode_connections = connOptions.m_masternode_connections;
     }
 
     CConnman(uint64_t seed0, uint64_t seed1, AddrMan& addrman, const NetGroupManager& netgroupman,
@@ -1928,6 +1932,7 @@ friend class CNode;
 
     /** Flag for activating masternode mode */
     bool m_active_masternode{false};
+    bool m_masternode_connections{true};
 
     SocketEventsMode socketEventsMode;
     std::unique_ptr<EdgeTriggeredEvents> m_edge_trig_events{nullptr};